1. Field of the Invention
The present invention relates to computer graphics systems, and more specifically to a system and method for automatically determining the signal parameters of an analog display signal received by a display unit of a computer system.
2. Related Art
Display units are often used in computer systems to display images. Typically, an image is sent to a display unit encoded in the form of an analog signal (e.g., RGB signals) and the display unit reproduces the image represented by the analog signal. For a proper reproduction of the image, it may be necessary to determine the signal parameters (explained below) of the analog signal.
In general, signal parameters are the values which enable a display unit to reproduce an image represented by the analog display signal. For example, as is well known in the art, an analog display signal can include several portions, with each portion representing a frame of an image. Each such portion can include several sub-portions, with each sub-portion representing a horizontal line. Several such horizontal lines together constitute a frame.
For an accurate reproduction of an image represented by an analog signal, a display unit may need to accurately determine the instances or points on an analog display signal which correspond to start positions ("horizontal start positions") of these horizontal lines and/or frames. Similarly, a display unit may need to determine other parameters such as vertical start position, height and width of an image for an accurate reproduction. Such parameters, which may be needed for accurate reproduction of an image are termed as display signal parameters in the present application.
Without such an accurate determination of one or more of the above noted parameters, a portion of an image may not be displayed on a screen of a display unit. As an illustration, if a horizontal start position is determined to be at a position later than a correct horizontal start position, some of the left portion of the horizontal line may not be displayed. On the other hand, if horizontal start position is determined to be at a position earlier than a correct horizontal start position, some of the right portion of the horizontal line may not be displayed.
Some prior systems attempt to use only a part of a digital display screen area as a matter of design so that inaccurate determination of a start position described above will not necessarily result in an image portion not being displayed. That is, under this scheme, if a start position is determined to be earlier or later than a correct start position, the sampled image may be displayed on a part of the display screen, which part may not be otherwise used if the start positions were to be correctly sampled. One problem with such a scheme is that the design employed there does not make full use of the display screen area under correct operating circumstances.
In an alternative scheme, a user is provided the option to manually adjust the start positions, height and width. Unfortunately, such manual schemes may be undesirable, particularly in consumer markets where the users may not be willing or sophisticated to use such manual features.
There are other display parameters which may be important for an accurate reproduction of an image represented by an analog display signal. Voltage swing of a digital to analog converter (DAC) is an example of such other display parameters. Voltage swing generally refers to the voltage values between the voltages used to represent maximum and minimum brightness levels of points of an image. DACs are typically situated in a computer system and generate analog display signals based on digital data representation of an image. Display units commonly receive these analog display signals and generate an image based on the received display signal.
The maximum and minimum values are typically defined by industry standards. However, manufacturing imperfections and inadequate testing often result in computer systems which have substantial deviation from the maximum and minimum voltage levels. As an illustration, according to RS-170 and VESA standards known in the art, minimum and maximum brightness levels are to be encoded in 0.0 V and 0.7 V respectively. However, these voltage levels can be in the range of 0.5 V to 1 V in typical implementations found in the market.
One problem with such deviations is that the resulting display quality may be sub-optimal. For example, if a display unit is designed to assume that maximum brightness is represented by 0.7 volts, but if a computer system generates a voltage level of 0.8 for maximum brightness, the graphics system may display all points having a voltage value above 0.7 at a maximum brightness level. Accordingly, highlight contrast is lost. On the other hand, if a computer system generates a voltage of 0.6 V (i.e., less than the correct voltage level) for the full brightness level, the full range of brightness levels possible on the display screen may not be fully utilized. In either case, the display quality is not optimal.
In some display units, a user is provided the ability to manually adjust the brightness level, and the display unit is designed to adjust the assumed voltage swing. However, the manual schemes are generally undesirable as users may not have the sophistication or desire or willingness to recognize the deviations from voltage swing levels. In addition, it may not be easy to perfectly adjust the assumed voltage swing levels manually in the display unit.
Therefore, what is needed is a scheme which enables an accurate and automatic determination of display signal parameters of an analog display signal received by a display unit.